The use of large area displays in foldable electronic devices is becoming increasingly interesting and this also creates growing interest towards different kinds of flexible display devices. Some solutions have been presented, inter alia, in U.S. Pat. No. 6,377,324, where the folding of a flexible display device has been taken into account; in U.S. Pat. No. 6,577,496, where the flexible display device is able to move; and in US 2004/0052044 A1, where a hinge system of an electronic device facilitates the flexing of a display device and the closing of the electronic device.
The manufacture, materials, structure and operation of flexible display devices are known as such in such respects how, for example, the structure allows the folding of a display device, as disclosed in US 2004/0159710 A1 and U.S. Pat. No. 6,016,176, or the rolling of a display device, as disclosed in U.S. Pat. No. 4,948,232, WO 2004/047059 A1 or US 2004/0061683 A1. The display device is based on, for example, LCD technique (Liquid Crystal Display) and they have been applied, inter alia, in mobile phones, as disclosed in WO 2004/001704 A1, US 2002/0090980 A1, U.S. Pat. No. 6,771,232 B2 or U.S. Pat. No. 6,311,076 B1.
In foldable electronic devices, such as wireless terminals, mobile phones and PDA devices (Personal Digital Assistant) the use of flexible display devices is problematic, when an integral display device is located twofold between the parts of an electronic device and covers the different parts of the opened electronic device. The electronic device is easy to close by folding the parts against each other, because the flexible display device may naturally tend to fold twofold. In the folded position said tendency is removed or decreases significantly, but in the open position of the electronic device, the above-mentioned effect may be directed towards the display device as a continuous tension. In addition to this, the phenomenon in question may limit the implementation possibilities of the electronic device, because its effect must be compensated in the construction of the hinge structure in order for the electronic device not to tend to close by itself. Lockings must possibly be added to the hinge or the device must be manually prevented from closing itself. Further, complex mechanical support arrangements are often required to ensure that the folding display remains flat and therefore easy to read when the device is opened.